Confused about wiring harness

I own a 67 the people I bought it from just basically chopped up the original wiring harness I am getting ready to start working on it and I want to know how to get a complete harness I’m confused because seems like a dome light lets say those couple of wires is called a harness. I was under the influence that a automotive wiring harness was a large amount of wires all together and each wire is terminated or landed in each own spot by reading the blueprints saying where each wire is ran to. I’m ignorant about alot with these cars but fast learner and motivated. If anyone could maybe point me in a direction or constructive criticism doesn’t matter. I don’t mind ya being a smart#&@ as long as I’m moving forward. Thanks for your time.

The main harness (underdash harness) is what you are most likely looking for. just about everything runs off your underdash harness, it has the fuse block and connections for ignition switch, radio, heater, dash cluster and your headlight and engine harness split off of that harness.
Cougar parts suppliers have used harness for sale. You should be able to find a wiring diagram on line for the car or you can purchase a Ford / Mercury shop manual for your Cougar. Good Luck

Make sure you’re getting the correct one for your car. XR7 and standard are different and not interchangeable. You have main harnesses like under dash, under hood and there are sub harnesses that attach to them like the door harness and the alternator harness. If you check out one of the retailers you’ll figure our which is which pretty easily.

Get your old harness rebuilt and tested. Then all of the Ford technical material will match your car. The wiring harness consists of many separate components. It has to be that way to allow the car to be build on an assembly line. It also allows for a bunch of different options to be installed or not installed. Many wires serve multiple purposes, some supply power to multiple devices some supply ground, and others are to interconnect supported systems. It is not a one-wire one-function thing.

Get a wiring diagram too if you don’t already have one. WCCC has them available for pdf download on their site.

I tried to download it twice and it came back not found.